Arbitrary function generator



MaY 20, 1958 J. T. sAwYER ETAL 2,835,773

ARBITRARY FUNCTION GENERATOR Filed April 29, 1957 2 Sheets-Sheet 2NVENTOR:

UnitedStates Patent O ARBITRARY FUNCTION GENERATOR James T. Sawyer andJohn Kellis Flora, Huntsville, Ala. Application April 29, 1957, SerialNo. 655,640

s claims. (ci. zur- 48) i This invention relates to an electrical devicedesignated as an arbitrary function generator. It has for its mainobjects to provide such a device that will be highly satisfactory forthe purpose intended, simple in structure, comparatively cheap tomanufacture, easy to use and keep in working condition, and extremelydurable.

Also the arbitrary function generator made according to this inventionaccomplishes the purpose of producing a voltage proportioned to theordinate of a curve drawn with special conducting ink or fluid on paperor other insulating material. The advantage of being able to produce avoltage directly from a curve drawn on paper is that this method ofpreparing a function for conversion to a voltage is very inexpensive,convenient, and quick.

yOther objects and advantages will appear from the drawings anddescription. p

By referring generally to the drawings, it will be observed that Fig, 1is a plan view of an arbitrary function generator made according to thepresent invention; Fig. 2 is a side elevational view of Fig. l; Fig. 3is an end elevational view of Fig. l; Fig. 4 is a circuit diagram of thegenerator; and Fig. 5 is a perspective viewofpparts of the deviceshowing the principle of operation.

Similar Vreference numerals refer to similar parts throughout theseveral views.

Referring to the drawings in detail it will be seen that the structureof the device comprises a rotable metal drum 1 which is adapted to bedriven by a suitable electric motor, a sheet of paper Z attached aroundthe drum, a curved line of electrically conductive ink 3 on the paper, awire-wound potentiometer 4 with a resistance preferably exceeding abouttwo thousand ohms, two rollers 5 made of ordinary metal plated with aprecious metal so that the surface of the rollers will not corrode, tothus maintain good electrical contact properties. Wires 6 are connectedas shown in Fig. 5. A main base 7 supports the side members S. The drumis mounted on a shaft 9 that is supported in bearings in the sidemembers. The drum is revolved by an electric motor 10 connected by chain11 and sprockets 12 'and 13. The side members are provided with slots 14in which the shaft ends 15, 16 and 17 of the potentiometer 4 and rollers5 are slidable. Springs 18, 19 and 20 are attached on studs 21, 22 and23 and are adapted to hold the potentiometer and rollers adjacent theink or fluid line on the paper on the drum. A spring type clip 24 holdsthe end of the paper on the drum.

Any suitable conductive ink may be used, such as Du Pont #4922 silverpaste or similar, butyl acetate or other suitable solvent, Sauereisen#P-l porcelain cement, or other nely ground inorganic filler; a smallamount of plastic such as polyethylene dissolved in the butyl acetatesolvent. The ink, when thinned to the proper consistency, ilows easilyand smoothly from an ordinary ruling pen, dries in about two minutes,and leaves a hard, durable line, which on the average is about im inchwide and is about .001 to .002 inch high. In the present invention thestraightness tolerances of the potentiometer roller,

contact rollers, and supporting surface of the drum are held much closerthan this, thus assuring continuous contact. The same ink or fluid curvecan be used many times, but will eventually wear out. Therefore thepresent type function generator is of greatest value where the inputfunction desired changes rather frequently, and it is for this typeapplication that it excels due to the ease and rapidity with which newink or` iluid curves can be prepared. Important features of .theinvention are that it is simple, convenient, and easy to operate. Italso accurately produces voltage proportional to the ordinate of almostany shape of curve that can be drawn including step functions. In thepast devices used to accomplish this purpose in this category haverelied upon the use of servo-positioned followers or the use of wireglued to paper or inserted in a groove in a drum with a sliding Contactmaintained between the wire and potentiometer. The disadvantages of theformer method are complexity, unreliability, possibility of the followerlosing the curve and the limitation on the shape of acceptable curves.The disadvantages of the latter method are inconvenience of attachingthe wire to the paper, or drum, the rapid wear on the potentiometer, thetendency toward noisy operation and the limitation on the shape ofacceptable curves. These disadvantages are eliminated in the presentinvention by utilizing direct rolling contact and an ink or fluid linewhich can be easily drawn to any shape de sired. It is also especiallyto be noted that a contact roller is located immediately to each side ofthe potentiometer roller, electrical continuity is required only betweenthe potentiometer roller and either one of the contact rollers.

The various parts of the device may be made of any material suitable forthe purpose, but we prefer to use materials generally used forsuchgpurposes. Also the parts may be made in different sizes andcapacities depending on how and where to be used.

While we have shown and described the preferred embodiment of ourinvention, we do not Wish to limit same to the exact and precise detailsof structure, and reserve the right to make all modifications andchanges so long as they remain within the scope of the invention and thefollowing claims.

Having described our invention we claim:

l. An arbitrary function generator of the class described comprising, amain supporting base, upward extending portions as sides attachedopposite eachother on the edge of the base, a shaft, said shaftsupported by bearings in said sides, a metal drum mounted on said shaft,a sheet of paper attached removably around on the circumference face ofsaid drum, a line of electric conductive ink upon said paper, said lineof ink starting at an edge of the paper at an end of the drum andextending on the paper and curved around the drum and ending at theother edge of the paper at the other edge of the drum, said ink being ofa quality to cause electric current to be transmitted thereby, the outerface of said ink line being slightly extended beyond the face of thepaper; a roller potentiometer mounted by its ends supported in slots insaid sides with its circumference face in contact with said ink line onsaid paper, springs attached to the ends of said roller potentiometeradapted to retain it in close contact with said ink line and paper, twocontact rollers mounted by their ends in slots in said sides, saidcontact rollers being positioned one along and near each side of saidpotentiometer, the circumference faces of said contact rollers being incontact with said ink line and paper, springs attached to the ends ofsaid contact rollers adapted to retain them in close contact with saidink line and paper; electric transmitting wires attached to said contactrollers; an electric motor mounted on said base and connected byvariable chains and gears driving means to said drum for revolving same;said conductive ink being adapted to complete an electric circuitbetween said roller potentiometer and said contact rollers when the drumis being revolved and the ink line surface is in contact with saidrollers.

2. An arbitrary function generator of the class described comprising, amain supporting base, upward extending sides attached opposite eachother on opposite edges of the base, a shaft, said shaft supported bybearings in said sides, a chart drum mounted cn said shaft, graph paperattached removably around on .the entire circumference face of the drum,a line of electric conductive ink upon said paper, said line of inkstarting at one edge of the paper and extending as a curve once aroundthe drum on the paper and ending at the other edge of the paper, theouter face of said ink line being slightly extended beyond the face ofthe paper; a roller potentiometer mounted vby its ends, said ends beingsupported in slots in said sides on the base with the circumference faceof the potentiometer in contact with said ink line on said paper,springs attached to the ends of the roller potentiometer adapted toretain it in close contact with said ink line and paper, two contactrollers mounted by their ends in slots in said sides, said contactrollers being disposed one along and near each side of saidpotentiometer, the circumference faces of said Contact rollers being incontact with said ink line and paper, springs attached to the ends ofsaid contact rollers for holding them in close contact with said inkline and paper; a plurality of electric transmitting wires removablyattached to said contact rollers; an electric motor mounted on said baseand connected by variable chains and gears as driving means to said drumshaft for revolving the drum at different speeds, said conductive inkbeing adapted to complete an electric circuit between said rollerpotentiometer and said contact rollers when the drum is being revolvedand the ink line surface is in contact with said rollers.

3. An arbitrary function generator of the class described having meansfor obtaining a voltage proportionate to the ordinate of a drawn curve,said means comprising, a main supporting base, upward extending sidesattached opposite each other on opposite edges of the base, a shaft andvbearings therefor, said shaft supported lll by the bearings in saidsides, a drum designated as a chart drum, said drum mounted on a shaftand bearings therefor, said shaft bearings mounted in said sides, asheet of graph paper attached removably around on the entirecircumference face of the drum, a line of electric conductive fluid uponsaid paper, said line of fluid starting at one edge of the paper at anend of the drum and extending in curve shape once around the drum and onthe paper and ending at the other edge of the paper at the opposite endof the drum, the outer face of said uid line being slightly extendedbeyond the face of the paper; a roller type potentiometer mounted by itsends, said ends being supported in slots in said sides on the base withthe circumference face of the potentiometer in contact with said fluidline on the paper, springs attached to the ends of the potentiometeradapted to retain it by tension of the springs in close contact withsaid fluid line and paper; twocontact rollers with shaft ends, slots insaid sides, said contact rollers mounted by the ends of their shafts insaid slots, said rollers being positioned one along and near each sideof said potentiometer, the circumference faces'of said contact rollersbeing in contact with said duid line and paper, springs attached to theshaft ends of said contact rollers, said springs by tension thereof`adapted to retain said contact rollers in close contact with said fluidline and paper; a plurality of electric current transmitting Wiresremovably attached to Said contact rollers; an electric motor mounted onsaid base and connected by variable chains and gears as driving means tosaiddrum shaft for revolving the drum at different speeds; said electricconductive line on the paper being adapted to complete an electriccircuit between said roller potentiometer and said contact rollers atany place along the fluid curved line when the drum is being revolvedand contacts are maintained between the faces of the three said rollersand the surface of the uid line.

References Cited in the tile of this patent UNTTED STATES PATENTSBromberg et al May 29, 1951 Brown Aug. 28, 1956

